(19)
(11) EP 0 868 022 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
18.04.2001 Bulletin 2001/16

(43) Date of publication A2:
30.09.1998 Bulletin 1998/40

(21) Application number: 98302377.1

(22) Date of filing: 27.03.1998
(51) International Patent Classification (IPC)7: H03F 3/08, H03F 1/30
(84) Designated Contracting States:
AT BE CH DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 28.03.1997 JP 7831097

(71) Applicant: SANYO ELECTRIC Co., Ltd.
Moriguchi-shi, Osaka (JP)

(72) Inventors:
  • Arai, Masashi
    Ora-gun, Gunma-ken (JP)
  • Nara, Masaaki
    Ora-gun, Gunma-ken (JP)
  • Seyama, Hiroki
    Ora-gun, Gunma-ken (JP)

(74) Representative: Cross, Rupert Edward Blount et al
BOULT WADE TENNANT, Verulam Gardens 70 Gray's Inn Road
London WC1X 8BT
London WC1X 8BT (GB)

   


(54) Offset correction circuit


(57) A current to voltage conversion circuit is formed of a differential amplifier circuit (1) with a negative input terminal connected to a light receiving element (3) and a register (4) which feeds back an output signal to the negative input terminal of the differential amplifier circuit (1) thereof. The variable gain amplifier circuit (5) amplifies the output voltage of the current to voltage conversion circuit to detect the bottom value of the output signal thereof. The comparator circuit (7) compares the bottom value with the reference value Vrl so that current flowing through the resistor (4) can be adjusted according to the difference between the bottom value and the reference value Vrl. The offset of the output signal from the variable gain amplifier circuit (5) supplied through the output terminal OUT is thereby adjusted. Since the peak value of the output signal of the variable gain amplifier circuit (5) is detected and the gain of the variable gain amplifier circuit (5) is controlled according to the difference between the peak value and the reference value Vr2, an output signal of a predetermined level can be obtained.






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